Halogenated flame retardants are used in rigid polyurethane foam insulation to ensure compliance with various flammability test protocols required by national, state, and local building code agencies. Halogenated flame retardants provide a cost-effective, efficient means to address performance criteria that have been made more difficult by substitution of hydrocarbon blowing agents for chlorofluorocarbons (CFC's), hydrochlorofluorocarbons (HCFC's), and expensive hydrofluorocarbons (HFC's).
Prior to concerns about the ozone depletion potential or global warming potential of halogenated blowing agents that had been commonly used in rigid foam insulation materials, it was relatively easy to obtain a Class A rating in ASTM E-84, “Standard Test Method for Surface Burning Characteristics of Building Materials” by simply using a halogenated blowing agent.
Under ASTM E-84, the test material must have a flame spread index (FSI) of 25 or less and a smoke-developed index (SDI) of 450 or less to attain a NFPA 101 Life Safety Code Class A designation. To attain a NFPA 101 Life Safety Code Class B designation under ASTM E-84, the test material must have a FSI less than or equal to 75 and an SDI of 450 or less.
The NFPA 101 Life Safety Code Class designations for ASTM-84 should not, however, be confused with the Class A, B, or C designations for ASTM E-108, “Standard Test Methods for Fire Tests of Roof Coverings”.
ASTM E-108 is a test designed to determine the resistance of an entire roof assembly, not just the foamed plastic, to an external fire from three perspectives—spread of flame, intermittent flame, and burning brand. Foams used for insulation and roof coverings applied to a steel deck require only flame spread testing.
Although only a Class B E-84 rating is generally needed for foamed plastic insulation for an insulated steel deck assembly to meet the ASTM E-108 requirements of section 1505.1 of the International Building Code (IBC), steel deck assemblies insulated with rigid polyurethane foam also must pass the more severe Factory Mutual Roof calorimeter portion of FM 4450. An FM 4450 designation of Class 1 for an insulated steel roof deck assembly means that the deck assembly meets Factory Mutual's criteria for internal fire resistance, wind uplift, live load resistances, corrosion of metal parts, and fatigue of plastic parts. Generally, foam formulation plays a significant role in passing the combustibility performance requirement of the test standard while the foam manufacturer product specifications and installation procedures determine if the roof assembly meets the other requirements of the FM 4450 standard. It would be expected that a rigid foam product that meets the combustibility requirement should readily obtain a Class 1 rating since it is well known in the industry how to properly specify and install the product. A Roof calorimeter is used to test for internal fire resistance. It is desirable to pass FM 4450 Roof calorimeter testing without using either a thermal barrier between the insulation and the steel decking of the 4½ ft×5 ft. (1.37 m×1.52 m) mock roofing assembly or a protective cover board on top of the insulation layer of the assembly. The Roof calorimeter test measures fuel contributions from combustible materials (e.g., asphalt) from the deck to the fire underneath it by simulating a fire inside a building. The net fuel contribution cannot exceed predetermined maximum values as a function of time.
The ASTM E-84 Tunnel test method provides a comparative evaluation of flame spread and smoke generation for 24 feet (7.3 m) long by 20 inch (50.8 cm) wide samples placed horizontally in a tunnel furnace and exposed to a gas flame that provides 5000 Btu/min of heat. This method was originally developed and published by Underwriters Laboratories as UL 723 in 1950 and adopted by ASTM as a formal test method in 1961. There is a specified draft flow to move the flame front toward the end of the tunnel during the 10 minute test period and the values measured for flame spread and smoke levels are indexed to those obtained for the conditioned red oak flooring calibration standard, whose flame front reaches the end of the specimen after 5½ minutes. For rigid foam samples, a rapid initial spread of flame to the specimen's maximum value in the first 60 seconds followed by a recession of the flame front is often observed. Since the test method requires that the maximum distance of flame travel be used in the calculation, the flammability of gaseous blowing agents and their concentration in the foam play a significant role in rigid foam performance in this test.
Halogenated organophosphorus flame retardants in combination with halogenated blowing agents have historically been used to produce foams exceeding an NFPA 101 E-84 Class B rating in this test. These ratings are presumably due to phosphorus acting predominantly in the condensed phase to produce a char barrier and the halogen acting as a radical scavenger in the vapor phase.
Use of more flammable hydrocarbon blowing agents has necessitated foam formulation changes. Generally, the formulation change has been to increase the level of halogenated organophosphorus flame retardant in the rigid foam.
Recent concerns about human health effects and the environmental impact of polybrominated diphenyl ethers (PBDEs) led California to pass legislation imposing a state-wide ban on these types of brominated flame retardants in 2003 and prompted Great Lakes Chemical Corporation to voluntarily phase out manufacture and importation of PBDEs into the U.S. in 2004. Subsequently, all halogenated flame retardants have come under greater public scrutiny and increased regulatory pressure.
Tris(2-chloroethyl) phosphate (TCEP) is no longer produced in Europe and may soon be banned in Canada from some household products and materials based on the Canadian government's Proposed Risk Assessment Approach for TCEP published in 2009.
A European Risk Assessment for the common flame retardant tris(2-chloro-1-methylethyl) phosphate (TCPP) that was published in 2008 concluded that currently no need exists for “further information and/or testing and no need for risk reduction measures beyond those which are being applied already” with regard to human health and safety. Nonetheless, a number of studies measuring levels of halogenated organophosphorus flame retardants in consumer products and household dust have since appeared in peer-reviewed journals.
Consequently, efforts to develop rigid polyurethane foam products that are free of halogenated blowing agents and halogenated flame retardants that meet the flammability requirements for NFPA 101 Life Security Code Class B ratings in ASTM E-84 testing and pass the FM 4450 Roof calorimeter test have increased.
In 1994, Nicola and Weber published the results of their evaluation of pentane, isopentane, and cyclopentane as blowing agents for use in the production of laminated boardstock rigid foam at the 35th Annual Polyurethane Technical/Marketing Conference in a paper entitled “Hydrocarbon Blown Foams for U.S. Construction Applications.” In this study, water was used as a co-blowing agent to minimize the pentane level. Chloroalkyl phosphate esters and brominated aromatic phthalate esters were used in combination with the water/pentane blowing agent to make polyisocyanurate rigid foam at a 240 index. These foams attained a Class A rating but did not meet key requirements for roofing applications in the Factory Mutual Roof calorimeter test (FM 4450). When the foam formulations were adjusted to meet this roofing requirement by increasing the index to 300, none of the tested samples were free of halogenated flame retardant.
Singh et al disclose a system for the production of rigid foam that meets NFPA 101 Class A rating in accordance with ASTM E-84 in U.S. Pat. No. 6,319,962. The Singh et al system includes an organic polyisocyanate, a polyfunctional isocyanate-reactive composition, less than about 1% by weight (based on total weight of the system) of water in combination with a hydrocarbon blowing agent, and at least one halogen-substituted phosphorus material. The halogen must be present at no more than 1.4% by weight of the total reactive system and the phosphorus is present at 0.3% to 2% by weight of the total reactive system.
Patent application U.S. 2006/0100295 describes an all liquid foam-forming system for rigid polyurethane foam that includes at least one liquid isocyanate or polyisocyanate, at least one aromatic polyester polyol, at least two halogenated flame retardants and water. The foam formed from this system has a density of at least 5 pounds per cubic foot (pcf) (80 kg/m3) and an ASTM E-84 Class A rating.
U.S. Pat. No. 4,797,428 broadly discloses that a rigid flame retardant foam having a Class A rating is formed as the reaction product of organic polyisocyanate, an isocyanate-reactive mixture composed of 25% to 75% of an oligoester that is the reaction product of a dicarboxylic acid semi-ester and an alkylene oxide, and a blowing agent. Only halogenated compounds are disclosed as blowing agents/flame retardants in the patent and patent examples.
Not one of the above-described disclosures teaches a process or foam-forming composition for the production of a rigid polyurethane foam free of added halogens that performs as a NFPA 101 Class B foam in ASTM E-84 and that also passes the FM 4450 Roof calorimeter test protocol.
U.S. Patent Application 2009/0156704 discloses rigid foam compositions that include halogen-free alkyl aryl phosphate esters as flame retardants in combination with mixtures of hydrocarbon blowing agents and water. The foams produced from these compositions are classified as B2 or “normal combustibility” in accordance with DIN 4102.
To meet the criteria for B2 in DIN 4102, the average maximum flame spread of 5 specimens measuring 90 mm×190 mm cannot exceed 150 mm during the 20 second test after exposure to a 20 mm flame from a small burner for the first 15 seconds of the test. Obviously these conditions differ markedly from those required for the ASTM E-84 Tunnel Testing described above.
There is no correlation between performance in DIN 4102 B2 and performance in ASTM E-84. No claims are made that the rigid foam systems disclosed in U.S. Patent Application 2009/0156704 meet both the NFPA 101 Class B E-84 standard and the Class 1 FM 4450 standard.
U.S. Patent Application 2009/0247657 describes improvement of the thermal stability of polyurethane-modified polyisocyanurate foam by combining high molecular weight ammonium polyphosphate with halogenated and non-halogenated flame retardants in the foam formulations. However, thermal stability is only determined by thermogravimetric analysis of foam samples in nitrogen, which has little bearing on performance upon exposure to a flaming ignition source such as in ASTM E-84.
U.S. Pat. No. 5,776,992 teaches that properly blended mixtures of nitrogen-containing and nitrogen-free polyols in combination with ammonium polyphosphate can produce foams with a B2 classification in the DIN 4102 test while either polyol type used separately with the flame retardant is classified as B3. There is no teaching or suggestion that these systems meet the Class B E-84 standard or that roof assemblies composed of rigid foams made with these systems will pass FM 4450.
Consequently, a need still exits for a rigid polyurethane foam system that does not include a halogenated flame retardant or a halogenated blowing agent and will pass both ASTM E-84 with a NFPA 101 Class B rating and FM 4450 Roof calorimeter testing.